1. Field of the Invention
This invention relates to an optical recording medium recording apparatus, and more particularly to an optical recording medium recording apparatus wherein an evaluation function which is used as an index to intensity adjustment of laser light when the laser light is irradiated to record information on an optical recording medium is adjusted in response to reflected light of the laser light.
2. Description of the Related Art
Various types of optical recording media such as optical disk on which digital information can be recorded are known in related art.
Particularly as write-once optical recording media which are formed using an organic coloring matter and on which digital information can be recorded once, a CD-R (Compact Disk Recordable), a DVD+R, a DVD-R (Digital Versatile Disk Recordable) and so forth are known. Meanwhile, as erasable type optical recording media which are formed using a phase-change type material and on which data can be rewritten, a CD-RW (Compact Disk ReWritable), a DVD-RW (Digital Versatile Disk ReWritable), a DVD-RAM (Digital Versatile Disk Random Access Memory), a BD-RE (Blu-ray Disk ReWritable) and so forth are known.
Although such optical recording media are usually fabricated on a production line which is managed strictly, a dispersion sometimes occurs with a coloring matter component or an alloy component from a difference among fabrication methods of different manufacturers or a dispersion between production lots.
Particularly a write-once optical recording medium formed using an organic coloring matter sometimes suffers from warping or surface deflection or the state of such warping or surface deflection sometimes changes depending upon the fabrication procedure or the use state or the storage state of the user. It is to be noted that the warping of the optical recording medium is a state wherein the optical recording medium is deformed like an open umbrella. Meanwhile, the surface deflection of the optical recording medium is a state that, when the optical recording medium is rotated, the recording face thereof is deflected laterally like undulations in response to the rotational angle.
If a dispersion of a coloring matter or an alloy component of a recording layer or an optical recording medium or warping or surface deflection of an optical recording medium occurs in this manner, then even if the manufacturer and the model of the optical recording medium are same, the recorded state of information on the recording face of the optical recording medium becomes different. Accordingly, upon reproduction of the information, fixed quality of the reproduction signal is not usually obtained, resulting in difficulty in decoding of the data.
Thus, as a method of adjusting the intensity of laser light to be used for recording on an optical recording medium in order that the quality of the reproduction signal may be kept fixed, various control methods are known including OPC (Optimum Power Calibration) and running OPC.
According to the OPC, before data are recorded, laser light of a predetermined pattern is irradiated upon a PCA (Power Calibration Area), which is a trial writing region of an optical recording medium, to perform trial writing. Then, the data written in this manner are reproduced and an optimum intensity of laser light is determined in accordance with a certain evaluation reference to enhance the recording quality.
Meanwhile, according to the running OPC, when laser light for recording is irradiated upon an optical recording medium to record required information, reflected light of the laser light is detected, and the intensity of the laser light to be irradiate is corrected in response the detected intensity of the reflected light.
The OPC and the running OPC are used such that, upon starting of recording of information on an optical recording medium, the OPC in the PCA of the optical recording medium is executed once and recording of information on the optical recording medium is started with the intensity of the laser light determined by the OPC. Thereafter, the intensity of the laser light is adjusted to an appropriate state by the running OPC.
It is to be noted that an optical recording medium is likely to suffer from a dispersion at inner and outer circumferential portions thereof in formation of a recording medium in a fabrication process, and the optimum intensity of laser light often differs along a diametrical direction of an optical recording medium.
In order to reflect such appropriate variation of the intensity of laser light at inner and outer circumferential portions of an optical recording medium, when the running OPC is performed, an evaluation function is used.
The evaluation function is represented by a characteristic curve which represents the depth information of a pit with respect to the intensity of laser light. In the running OPC, the intensity of laser light is adjusted based on the characteristic curve so that information can be written with high quality on the optical recording medium.
It is to be noted that, although, in the running OPC, reflected light of laser light upon recording of information on an optical recording medium with the laser light is detected to perform intensity adjustment of the laser light, since the reflected light detected is different from reflected light upon reading out of the recorded information, there is the possibility that the reflected light may not reflect the recorded state correctly.
Thus, also such a countermeasure as described just below is available recently so that a recording process can be executed using laser light of a more appropriate intensity. In particular, a recording process of information on an optical recording medium is interrupted while it is proceeding, and information recorded before such interruption is reproduced and intensity adjustment of the laser light is performed based on a result of detection of reflected light upon reproduction to reproduce the recording process. A method of the type described is disclosed, for example, in Japanese Patent Laid-Open No. 2004-234812.